Places to start:
- National World War II Museum - Propaganda Search Results
- PBS - ‘I won’t eat no more ice cream’ and other propaganda posters of WWI
- 50 Powerful Examples of Visual Propaganda and the Meanings Behind Them
- BEWARE: This site doesn't necessarily give you all the information you might need to cite the Propaganda Poster that you choose. Use the Google Image search to find the rest of the information for the poster. This may not be the article you cite for your poster.